Tuning sizes, morphologies, and magnetic properties of monocore versus multicore iron oxide nanoparticles through the control addition of water in the polyol synthesis

The polyol route is a versatile and up-scalable method to produce large batches of iron oxide nanoparticles with well-defined structures and magnetic properties. Importance of parameters such as temperature and reaction time, heating profile, nature of polyol solvent or of organometallic precursors on nanostructure and properties has already been described in the literature. Yet, the crucial role of water in the forced hydrolysis pathway has never been reported despite its mandatory presence for nanoparticle production. This communication investigates the influence of the water amount and temperature at which it is injected in the reflux system for either a pure polyol solvent system or a mixture with poly(hydroxy)amine. Distinct morphologies of nanoparticles were thereby obtained, from ultra-ultra-small smooth spheres down to 4 nm in diameter to larger ones up to 37 nm. Well-defined multi-core assemblies with narrow grain size dispersity termed nanoflowers were also synthesized. A diverse and large library of samples was obtained by playing with the nature of solvents and amount of added water while keeping all other parameters constant. The different morphologies lead to magnetic nanoparticles suitable for important biomedical applications such as magnetic hyperthermia, MRI contrast agent, or both.